#! /usr/bin/perl -w
use strict;

my @dist = dice_distribution(
  sides => 6,
  number => 4,
  slice => [1, 2, 3],
);

my $average = sum( map $_*$dist[$_], 0..$#dist ) / sum(@dist);
print "The average is $average\n";

sub dice_distribution {
  my %args = @_;

  my $sides = $args{sides} || 6;
  my $number = $args{number} || 3;
  my $slice = $args{slice} || [0..($number - 1)];

  my @distribution;
  nested_for(
    sub {
      my @dice = (sort {$a <=> $b} @_)[@$slice];
      $distribution[ sum(@dice) ]++;
    }, map [1..$sides], 1..$number,
  );
  # Quiet warnings
  $_ ||= 0 for @distribution;
  return @distribution;
}

sub sum {
  my $sum = 0;
  $sum += $_ for @_;
  return $sum;
}

sub nested_for {
  bind_loops(@_)->();
}

sub bind_loops {
  my $fn = shift;
  my $range = shift;
  my $sub = sub {$fn->($_, @_) for @$range};
  return @_ ? bind_loops($sub, @_) : $sub;
}